Method for making electrothermal actuators

ABSTRACT

A method for making an electrothermal actuator requires a carbon nanotube paper being provided. The carbon nanotube paper is cut along a cutting-line to form a patterned carbon nanotube paper. At least two electrodes are formed on the patterned carbon nanotube paper. Finally, the electrothermal actuator is obtained by forming a flexible polymer layer on the patterned carbon nanotube paper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201410351924.6, filed on Jul. 23, 2014 inthe China Intellectual Property Office, disclosure of which isincorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a method for making electrothermalactuators.

2. Description of Related Art

Conventional electrothermal actuator is a membrane structure of whichmain material is polymer. When a current is applied, a temperature ofthe polymer is increased, which can lead to a sensible volume expansionof the polymer, and then the membrane structure bends and theelectrothermal actuator is activated. Thus, electrode materials of theelectrothermal actuator are required to be excellent conductive,flexible, and thermally stable due to its operating principle.

Composite materials containing carbon nanotubes are conductive andalready being used for electrothermal actuators. When a current isapplied, the electrothermal composite materials containing carbonnanotubes can generate heat. Then a volume of the electrothermalcomposite materials containing carbon nanotubes is expanded and theelectrothermal composite materials are bended. Electrothermal actuatorsobtained by conventional methods containing carbon nanotubes include aflexible polymer matrix and carbon nanotubes dispersed in the flexiblepolymer matrix. However, a deformation of conventional electrothermalactuators containing carbon nanotubes is not large enough, and aresponse rate of conventional electrothermal actuators is slow, whichare not beneficial to practical application.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures.

FIG. 1 shows a schematic structural view of one embodiment of anelectrothermal composite material.

FIG. 2 shows a schematic of a first embodiment of an electrothermalcomposite material before and after electrifying.

FIG. 3 shows a schematic structural view of a second embodiment of anelectrothermal actuator.

FIG. 4 shows a schematic structural view of a third embodiment of anelectrothermal actuator.

FIG. 5 shows a schematic structural view of a third embodiment of anelectrothermal actuator with different shape.

FIG. 6 shows a schematic structural view of a third embodiment of anelectrothermal actuator with a plurality of electrodes.

FIG. 7 shows a schematic structural view of a fourth embodiment of anelectrothermal actuator.

FIG. 8 shows a schematic structural view of a fifth embodiment of anelectrothermal actuator.

FIG. 9 shows a schematic structural view of a fifth embodiment of anelectrothermal actuator with different shape.

FIG. 10 shows a schematic structural view of a fifth embodiment of anelectrothermal actuator with a plurality of conductive paths.

FIG. 11 shows a flow chart of one embodiment of a method of making anelectrothermal actuator.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts havebeen exaggerated to better illustrate details and features of thepresent disclosure.

Several definitions that apply throughout this disclosure will now bepresented.

The term “substantially” is defined to be essentially conforming to theparticular dimension, shape or other feature that the term modifies,such that the component need not be exact. For example, “substantiallycylindrical” means that the object resembles a cylinder, but can haveone or more deviations from a true cylinder. The term “comprising,” whenutilized, means “including, but not necessarily limited to”; itspecifically indicates open-ended inclusion or membership in theso-described combination, group, series and the like.

Referring to FIG. 1, a first embodiment of an electrothermal compositematerial 100 includes a flexible polymer layer 140 and a carbon nanotubepaper 120. The carbon nanotube paper 120 is stacked on the flexiblepolymer layer 140 and at least partly embedded into the flexible polymerlayer 140. A thermal expansion coefficient of the flexible polymer layer140 is greater than or equal to ten times that of the carbon nanotubepaper 120. In one embodiment, the thermal expansion coefficient of theflexible polymer layer 140 is greater than or equal to one hundred timesthat of the carbon nanotube paper 120.

A thickness of the carbon nanotube paper 120 is in a range from about 30micrometers to about 50 micrometers. A conductivity of the carbonnanotube paper 120 along a first direction parallel to a surface of thecarbon nanotube paper 120 is in a range from about 1000 S/m to about6000 S/m. When the conductivity of the carbon nanotube paper 120 alongthe first direction is too large, such as greater than 6000 S/m, if apredetermined voltage (such as 10V) is applied to the carbon nanotubepaper 120, the carbon nanotube paper 120 can not generate enough heat tocause the thermal expansion and deformation of the flexible polymerlayer 140. When the conductivity of the carbon nanotube paper 120 alongthe first direction is too small, such as less than 1000 S/m, if thepredetermined voltage is applied to the carbon nanotube paper 120, athermal response rate of the electrothermal composite material 100 willbe too slow. In one embodiment, the conductivity of the carbon nanotubepaper 120 along the first direction is in a range from about 2000 S/m toabout 3500 S/m. A density of the carbon nanotube paper 120 can begreater than or equal to 0.5 g/cm³, thus, a tensile strength of thecarbon nanotube paper 120 can be greater than 3 Mpa. When the density ofthe carbon nanotube paper 120 is less than 0.5 g/cm³, the tensilestrength of the carbon nanotube paper 120 is too small to be easilydisrupted during the thermal expansion and deformation of the flexiblepolymer layer 140. In one embodiment, the density of the carbon nanotubepaper 120 is greater than or equal to 0.5 g/cm³ and less than or equalto 1.2 g/cm³.

The carbon nanotube paper 120 includes a plurality of carbon nanotubesextending substantially along the same direction and joined end-to-endby Van der Waals attractive force. The plurality of carbon nanotubes areparallel to the surface of the carbon nanotube paper 120. An anglebetween an extending direction of the plurality of carbon nanotubes andthe first direction is in a range from about 45° to about 90°,therefore, the electrical conductivity of the carbon nanotube paper 120along the first direction is in the range from about 1000 S/m to about6000 S/m. In one embodiment, the angle between the extending directionof the plurality of carbon nanotubes and the first direction ranges fromabout 80° to about 90°.

In one embodiment, the carbon nanotube paper 120 is rectangular with alength of 6 centimeters, a width of 3 centimeters, and a thickness of 30micrometers. The tensile strength of the carbon nanotube paper is about4 Mpa. The density of the carbon nanotube paper 120 is about 1.0 g/cm³.And the angle between the extending direction of the plurality of carbonnanotubes and the first direction is about 90°.

The flexible polymer layer 140 can be a sheet with a thickness rangingfrom about 270 micrometers to about 450 micrometers to meet the needs ofboth large deformation and high thermal response rate. The flexiblepolymer layer 140 can be overlapped with the carbon nanotube paper 120.A material of the flexible polymer layer 140 can have a good shapememory effect and an excellent thermal property. The flexible polymerlayer 140 has an original shape at a starting temperature. The shapememory effect refers to that when the temperature of the flexiblepolymer layer 140 is higher than a certain temperature, the flexiblepolymer layer 140 deforms, and when the temperature of the flexiblepolymer layer 140 returns to the starting temperature, the flexiblepolymer layer 140 returns to the original shape. The material of theflexible polymer layer 140 can be silicone rubber, poly methylmethacrylate, polyurethane, epoxy resin, poly ethyl acrylate,polystyrene, polybutadiene, polyacrylonitrile, polyaniline, polypyrrole,polythiophene or combinations thereof. In one embodiment, the flexiblepolymer layer 140 is a silicone rubber membrane with a thickness of 300micrometers and a thermal expansion coefficient of 3.1×10⁻⁴/K.

A thickness ratio of the carbon nanotube paper 120 and the flexiblepolymer layer 140 can be in a range from about 1:7 to about 1:10. If thethickness ratio is too small, such as less than 1:10, a temperature riseof the flexible polymer layer 140 will be too slow when it is heated bythe carbon nanotube paper 120, thus, the thermal response rate of theelectrothermal composite material 100 will be too slow. If the thicknessratio is too great, such as greater than 1:7, a difference of thermalexpansion quantities between the carbon nanotube paper 120 and theflexible polymer layer 140 will be too small due to that the thermalexpansion quantity is proportion to both the thermal expansioncoefficient and a volume, thus, the deformation of the electrothermalcomposite material 100 will be too small. In one embodiment, thethickness ratio of the carbon nanotube paper 120 and the flexiblepolymer layer 140 is about 1:9.

When the electrothermal composite material 100 is in application, thepredetermined voltage is applied to the carbon nanotube paper 120, acurrent is transmitted through a conductive network formed by theplurality of carbon nanotubes. The carbon nanotube paper 120 convertsthe electric energy to heat, thereby heating and expanding the flexiblepolymer layer 140. The thermal expansion coefficients of the flexiblepolymer layer 140 and the carbon nanotube paper 120 are different, sothat the electrothermal composite material 100 bends in a directionoriented to the carbon nanotube paper 120 which has a smaller thermalexpansion coefficient. The thermal response rate of the electrothermalcomposite material 100 is less than ten seconds. The electrothermalcomposite material 100 can be bent 180° within ten seconds. Theelectrothermal composite material 100 can repeatedly bend over 10,000times due to the excellent mechanical properties of the carbon nanotube.

Referring to FIG. 2, in one embodiment, a voltage of 20V and a currentof 0.2 A are applied by a power source to the electrothermal compositematerial 100 through conduct wires. The electrothermal compositematerial 100 bends 180° to the side of the carbon nanotube paper 120within 8 seconds.

Referring to FIG. 3, a second embodiment of an electrothermal actuator10 includes an operating portion 102 and two electrodes 112. Theoperating portion 102 is a long strip formed by cutting theelectrothermal composite material 100. The operating portion 102 atleast partially extends along the first direction. The extendingdirection of the plurality of carbon nanotubes is substantiallyperpendicular to a longitudinal direction of the operating portion 102.The conductivity of the operating portion 102 along the longitudinaldirection is about 3000 S/m, and the conductivity of the operatingportion 102 along the extending direction of the plurality of carbonnanotubes is about 30000 S/m. An extending direction of the twoelectrodes 112 is substantially perpendicular to the longitudinaldirection of the operating portion 102. The two electrodes 112 areparallel to and spaced apart from each other. The two electrodes 112 canbe located on opposite ends of the operating portion 102 along thelongitudinal direction and electrically connected with the carbonnanotube paper 120.

The two electrodes 112 can be made of metal, carbon nanotubes,conductive silver paste or any other suitable conductive materials. Theconductive property of the two electrodes 112 is substantiallyunaffected by the bend of the operating portion 102. In one embodiment,the two electrodes 112 are made of conductive flexible material such asmetal, carbon nanotubes or conductive silver paste. The number of theelectrodes 112 is not limited to two and can be set as desired.

During an operation of the electrothermal actuator 10, a voltage isapplied to the two electrodes 112. A current flow through the operationportion 102 along the longitudinal direction. The operation portion 102converts the electric energy to heat. Since the conductivity of theoperating portion 102 along the longitudinal direction is about 3000S/m, the electrothermal actuator 10 can bend quickly along thelongitudinal direction.

Referring to FIG. 4, a third embodiment of an electrothermal actuator 20includes two operating portions 202 and two electrodes 212. The twooperating portions 202 are connected with each other to form an L-shapestructure with a conductive path, wherein each operating portions 202 isa long strip obtained by cutting the electrothermal composite material100. The two electrodes 212 are respectively located on two ends of theL-shape structure and electrically connected with the conductive path.Thus, a current can be introduced to the L-shape structure via the twoelectrodes 212.

Each of the two operating portions 202 includes a plurality of carbonnanotubes extending substantially along the same direction and joinedend-to-end by Van der Waals attractive force in the extending direction.An angle between the extending direction of the plurality of carbonnanotubes and a current direction is about 45°. Thus, a conductivity ofeach operating portions 202 along the current direction is in a rangefrom about 1000 S/m to about 6000 S/m. When a predetermined voltage isapplied to the two electrodes 212, the two operating portions 202 cangenerate heat and respectively bend along the current direction.

The electrothermal actuator 20 can also include at least three operatingportions 202 as shown in FIG. 5, and the at least three operatingportions 202 can be connected with each other to form differentstructures as long as the conductivity of each operating portions 202along the current direction is in the range from about 1000 S/m to about6000 S/m. Multifunctional actuation can be realized by electrothermalactuators 20 with the different structures formed by the at least threeoperating portions 202.

The structure formed by the at least two operating portion 202 can haveat least two conductive paths, and more than two electrodes 212. The atleast two conductive paths are electrically connected in parallel asshown in FIG. 6. The electrothermal actuator 20 includes two operatingportions 202 and three electrodes 212. The two operating portions 202are connected with each other to form a T-shape structure with twoconductive paths, and the three electrodes 212 are located on three endsof the T-shape structure and electrically connected to the twoconductive paths in parallel.

The structure formed by the at least two operating portions 202 can bean integrated structure obtained by cutting the electrothermal compositematerial 100. The at least two operating portions 202 can also be gluedtogether by a conductive adhesive. In one embodiment, each of theflexible polymer layer 140 and the carbon nanotube paper 120 of theelectrothermal actuators 20 is an integrated structure.

The angle between the extending direction of the plurality of carbonnanotubes and the current direction, in each of the at least twooperating portions 202, is not limited to about 45°, as long as theconductivity of each operating portions 202 is in the range from about1000 S/m to about 6000 S/m along the current direction. In oneembodiment, the angle between the extending direction of the pluralityof carbon nanotubes and the current direction, in each of the at leasttwo operating portions 202, is in a range from about 45° to about 90°.In another embodiment, the angle between the extending direction of theplurality of carbon nanotubes and the current direction, in each of theat least two operating portions 202, is in a range from about 80° toabout 90°.

Referring to FIG. 7, a fourth embodiment of an electrothermal actuator30 includes a long strip operating portion 302 and two electrodes 312.The long strip operating portion 302 consecutively bends along a firstdirection and a second direction to form a “

” shape conductive path. The two electrodes 312 are respectively locatedon two ends of the long strip operating portion 302 and electricallyconnected with the “

” shape conductive path. Thus, a current can be introduced to the “

” shape conductive path via the two electrodes 312.

The long strip operating portion 302 is obtained by cutting theelectrothermal composite material 100. The long strip operating portion302 includes a plurality of carbon nanotubes extending substantiallyalong the same direction, and joined end-to-end by Van der Waalsattractive force in the extending direction. The first direction issubstantially perpendicular to the second direction. A first anglebetween the extending direction of the plurality of carbon nanotubes andthe first direction is about 45°. A second angle between the extendingdirection of the plurality of carbon nanotubes and the second directionis about 45°. Thus a conductivity of the long strip operating portion302 along the first direction and the second direction are both in arange from about 1000 S/m to about 6000 S/m. When a predeterminedvoltage is applied, a first segment of the long strip operating portion302 extending along the first direction will bend along the firstdirection, and a second segment of the long strip operating portion 302extending along the second direction will bend along the seconddirection.

The first direction is not limited to be perpendicular to the seconddirection, and the first angle and the second angle are not limited tobe 45°, as long as the conductivity of the long strip operating portion302 along the first direction and the second direction are both in therange from about 1000 S/m to about 6000 S/m. In one embodiment, each ofthe first angle and the second angle is in a range from about 45° toabout 90°. In one embodiment, each of the first angle and the secondangle is in a range from about 80° to 90°.

The conductive path formed by the long strip operating portion 302 isnot limited to the “

” shape. Conductive paths with different shapes can be selectedaccording to need.

Referring to FIG. 8, a fifth embodiment of an electrothermal actuator 40includes two operating portions 402, a connecting portion 404 and twoelectrodes 412. Each of the two operating portions 402 and theconnecting portion 404 are respectively a long strip obtained by cuttingthe electrothermal composite material 100. The two operating portions402 are parallel to and spaced apart from each other, and furtherelectrically connected with each other by the connecting portion 404.The two operating portions 402 and the connecting portion 404 togetherdefine a U-shape structure with a conductive path. The U-shape structurecan be an integrated structure obtained by cutting the electrothermalcomposite material 100. The two electrodes 412 are respectively locatedon two ends of the U-shape structure. A current can be introduced to theconductive path via the two electrodes 412.

Each of the two operating portions 402 and the connecting portion 404includes a plurality of carbon nanotubes extending substantially alongthe same direction and joined end-to-end by Van der Waals attractiveforce in the extending direction. A first angle between a firstextending direction of the plurality of carbon nanotubes in each of thetwo operating portions 402 and a current direction is about 90°, thus aconductivity of each of the two operating portions 402 along the currentdirection is in a range from about 1000 S/m to about 6000 S/m. A secondangle between a second extending direction of the plurality of carbonnanotubes in the connecting portion 404 and the current direction isabout 0°, thus a conductivity of the connecting portions 404 along thecurrent direction is greater than 6000 S/m. The first extendingdirection of the plurality of carbon nanotubes in each of the twooperating portions 402 can be same with the second extending directionof the plurality of carbon nanotubes in the connecting portion 404.

The connecting portion 404 is only used to electrically connect the twooperating portions 402. The connecting portion 404 has excellentconductivity more than 6000 S/m. Thus, small heat is generated by theconnecting portion 404 when the current is introduced and the connectingportion 404 cannot bend along the current direction. Therefore, theactuating direction of the electrothermal actuator 40 only depends on abend direction of the two operating portions 402. When the current isintroduced to the conductive path via the two electrodes 412, the twofree ends of the two operating portions 402 away from the connectingportion 404 can be fixed, thus the two operating portions 402 can bendalong a direction from the end connected with the connecting portion 404to the free end away from the connecting portion 404. Thus, theelectrothermal actuator 40 with the U-shape structure can be actuatedalong lengthways.

The first angle between the first extending direction of the pluralityof carbon nanotubes in each of the two operating portions 402 and thecurrent direction is not limited to 90°, as long as the conductivity ofeach of the two operating portions 402 along the current direction is inthe range from about 1000 S/m to about 6000 S/m. In one embodiment, thefirst angle between the first extending direction of the plurality ofcarbon nanotubes in each of the two operating portions 402 and thecurrent direction is in a range from about 45° to about 90°. In oneembodiment, the first angle between the first extending direction of theplurality of carbon nanotubes in each of the two operating portions 402and the current direction is in a range from about 80° to about 90°.

The second angle between the second extending direction of the pluralityof carbon nanotubes in the connecting portions 404 and the currentdirection is not limited to 0°, as long as the conductivity of theconnecting portions 404 along the current direction is greater than 6000S/m. In one embodiment, the second angle between the second extendingdirection of the plurality of carbon nanotubes in the connectingportions 404 and the current direction is more than or equal to 0° andless than 45°. In one embodiment, the second angle between the secondextending direction of the plurality of carbon nanotubes in theconnecting portions 404 and the current direction is in a range fromabout 0° to about 10°.

The electrothermal actuator 40 can also include at least three operatingportions 402, at least two connecting portion 404 and at least threeelectrodes 412. The at least three operating portions 402 and the atleast two connecting portions 404 can define different structures, aslong as the conductivity of each of the at least three operatingportions 402 along the current direction is in the range from about 1000S/m to about 6000 S/m, and the conductivity of the at least twoconnecting portions 404 along the current direction is more than 6000S/m.

Referring to FIG. 9, the electrothermal actuator 40 includes a pluralityof operating portions 402, a plurality of connecting portions 404 andtwo electrodes 412. Each of the plurality of operating portions 402 andeach of the plurality of connecting portions 404 are respectively a longstrip obtained by cutting the electrothermal composite material 100. Theplurality of connecting portions 404 is used to connect the plurality ofoperating portions 402 with each other and to connect the plurality ofoperating portions 402 with the two electrodes 412. The plurality ofoperating portions 402 and the plurality of connecting portions 404define a T-shaped structure together with a conductive path. TheT-shaped structure can be an integrated structure obtained by cuttingthe electrothermal composite material 100. The two electrodes 412 arelocated on two ends of the T-shaped structure to introduce a current tothe conductive path.

Each of the plurality of operating portions 402 includes a plurality ofcarbon nanotubes extending substantially along the same direction andjoined end-to-end by Van der Waals attractive force in the extendingdirection. A first angle between the first extending direction of theplurality of carbon nanotubes in each of the plurality of operatingportions 402 and a current direction is about 90°. A second anglebetween the second extending direction of the plurality of carbonnanotubes in the plurality of connecting portion 404 and the currentdirection is about 0°. The first extending direction of the plurality ofcarbon nanotubes in each of the plurality of operating portions 402 canbe same with the second extending direction of the plurality of carbonnanotubes in each of the plurality of connecting portions 404. When thecurrent is introduced to the conductive path via the two electrodes 412,the plurality of operating portions 402 can be bent from both ends tothe center, and the electrothermal actuator 40 with the T-like structurecan be actuated along a transverse direction.

The operating portion 402 and the connecting portion 404 can definedifferent conductive paths with different shapes, thereby achievingdifferent bend actuator.

The operating portion 402 and the connecting portion 404 can also format least two conductive paths. The at least two conductive paths areelectrically connected in parallel or in series.

Referring to FIG. 10, the electrothermal actuator 40 includes aplurality of operating portions 402, a plurality of connecting portions404 and three electrodes 412. The plurality of operating portions 402and the plurality of connecting portions 404 are connected to form twoconductive paths. The three electrodes 412 are located on the twoconductive paths and spaced from each other. The three electrodes 412can introduce current to the two conductive paths at the same time tomake the two conductive paths being electrically connected in parallel.

Each of the plurality of operating portions 402 extends along a firstdirection, and each of the plurality of connecting portions 404 extendsalong a second direction. The conductivity of each of the plurality ofoperating portions 402 along the first direction is in the range fromabout 1000 S/m to about 6000 S/m, and the conductivity of the pluralityof connecting portions 404 along the second direction is more than 6000S/m. A first angle between the first extending direction of theplurality of carbon nanotubes in the operating portions 402 and thefirst direction is more than or equal to 45° and less than 90°. A secondangle between the second extending direction of the plurality of carbonnanotubes in the connecting portions 404 and the second direction ismore than or equal to 0° and less than 45°.

FIG. 11 illustrates one embodiment of a method for making anelectrothermal actuator, which includes the following steps:

S1: providing a carbon nanotube paper, wherein the carbon nanotube paperincludes a plurality of carbon nanotubes extending along the samedirection and joined end to end by van der Waals attractive force, and adensity of the carbon nanotube paper can be greater than or equal to 0.5g/cm³;

S2: cutting the carbon nanotube paper along a cutting-line to form apatterned carbon nanotube paper, wherein an angle between an extendingdirection of the plurality of carbon nanotubes and at least a portion ofthe cutting-line is in a range from about 45 degrees to about 90degrees;

S3: forming at least two electrodes on the patterned carbon nanotubepaper; and

S4: forming a flexible polymer layer on the patterned carbon nanotubepaper, wherein the patterned carbon nanotube paper is at least partlyembedded into the flexible polymer layer, a thickness ratio of thecarbon nanotube paper and the flexible polymer layer is in a range fromabout 1:7 to about 1:10, and a thermal expansion coefficient of theflexible polymer layer is greater than or equal to ten times that of thecarbon nanotube paper.

In step S1, a method for making the carbon nanotube paper includes thefollowing steps:

S11: providing a roller and a pressing device, wherein the roller has anaxis, the pressing device has a pressing surface opposing to the roller,and the pressing surface is parallel to the axis of the roller;

S12: providing a carbon nanotube array, forming a carbon nanotube filmstructure by drawing a plurality of carbon nanotubes from the carbonnanotube array, and fixing the carbon nanotube film structure to theroller;

S13: spinning the roller to wind the carbon nanotube film structure tothe roller, the pressing device grinds or presses the carbon nanotubefilm structure to compact the carbon nanotube film structure and obtainthe carbon nanotube paper.

The thickness and strength of the carbon nanotube paper can becontrolled by the number of the carbon nanotube film. Examples ofmethods for making carbon nanotube papers are taught by U.S. Pat. No.9,017,503 to Zhang et al.

In one embodiment, the thickness of the carbon nanotube paper is in arange from about 30 micrometers to about 50 micrometers. A conductivityof the carbon nanotube paper along the extending direction of theplurality of carbon nanotubes is about 3000 S/m, and a conductivityalong a direction perpendicular to the extending direction of theplurality of carbon nanotubes is about 30000 S/m.

In step S2, The patterned carbon nanotube paper can be L-shape, U-shape,“†” shape, palm shape, or other shapes. The cutting-line can be a curvedline or a folded line. The cutting-line extends along a first directionand an second direction, the seventh direction and the eighth directioncan be perpendicular to each other.

In one embodiment, an angle of the extending direction of the carbonnanotubes and the first direction is about 45 degrees, and an angle ofthe extending direction of the carbon nanotubes and the second directionis about 45 degrees; therefore, the conductivity of the patterned carbonnanotube paper along the first direction and the second direction areboth ranged from about 1000 S/m to about 6000 S/m. In anotherembodiment, the angle of the extending direction of the carbon nanotubesand the first direction is about 90 degrees, an angle of the extendingdirection of the carbon nanotubes and the second direction is about 0degree; therefore, the conductivity of the patterned carbon nanotubepaper along the seventh direction is ranged from about 1000 S/m to about6000 S/m, and the conductivity of the patterned carbon nanotube paperalong the eighth direction is greater than 6000 S/m. In one embodiment,the cutting-line is closed to form a conductive path.

In one embodiment, the carbon nanotube paper is cut by laser.

In step S3, at least two electrodes adhered to the patterned carbonnanotube paper via conductive adhesive. The conductive adhesive can beselected from silver conductive adhesive, gold conductive adhesive,copper conductive adhesive, carbon-based conductive adhesive orcombination thereof. In one embodiment, the conductive adhesive isconductive silver paste.

In step S4, a method for forming the flexible polymer layer on thepatterned carbon nanotube paper includes the following steps:

S41: putting the patterned carbon nanotube paper in a mold;

S42: injecting a flexible polymer prepolymer, which is in aviscous-liquid state, into the mold; wherein the patterned carbonnanotube paper is completely immersed in the flexible polymerprepolymer;

S43: solidifying the flexible polymer prepolymer to form the flexiblepolymer layer; and removing the mold; and

S44: removing part of the flexible polymer layer that is not overlappedwith the patterned carbon nanotube paper along edges of the patternedcarbon nanotube paper.

In step S41, the putting the patterned carbon nanotube paper in the moldincludes coating a release agent on an inner surface of the mold. Therelease agent is propitious to remove the mold.

In step S42, the material of the flexible polymer prepolymer can besilicone rubber prepolymer, poly methyl methacrylate prepolymer,polyurethane prepolymer, epoxy resin prepolymer, poly ethyl acrylateprepolymer, polystyrene prepolymer, polybutadiene prepolymer,polyacrylonitrile prepolymer, polyaniline prepolymer, polypyrroleprepolymer, polythiophene prepolymer or combinations thereof. In oneembodiment, the flexible polymer prepolymer is silicone rubberprepolymer.

The carbon nanotube paper can include a plurality of micropores and theflexible polymer prepolymer can permeate in the micropores of the carbonnanotube paper. Thus the carbon nanotube paper can be at least partlyembedded into the flexible polymer layer and combined with the flexiblepolymer layer closely.

In one embodiment, the flexible polymer prepolymer is deaerated beforesolidifying. A method for deaerating the flexible polymer prepolymer canbe vacuum deaeration.

In step S43, a method for solidifying the flexible polymer prepolymercan be heating.

A thickness of the flexible polymer layer is ranged from about 270micrometers to about 450 micrometers. If the thickness is too large, atemperature rise of the flexible polymer layer will be too slow when itis heated by the carbon nanotube paper, thus, the thermal response rateof the electrothermal composite material will be too slow. If thethickness is too small, a difference of thermal expansion quantitiesbetween the carbon nanotube paper and the flexible polymer layer will betoo small due to that the thermal expansion quantity is proportion toboth the thermal expansion coefficient and a volume, thus, thedeformation of the electrothermal composite material 100 will be toosmall.

A thickness ratio of the carbon nanotube paper and the flexible polymerlayer can be in a range from about 1:7 to about 1:10. In such range thethermal response rate of the electrothermal actuator is high, and thedeformation of the electrothermal actuator is large. In one embodiment,the thickness ratio of the carbon nanotube paper and the flexiblepolymer layer is about 1:9.

The flexible polymer layer has substantially the same shape as that ofthe patterned carbon nanotube paper.

The electrothermal composite material and the electrothermal actuatorcan be used for artificial muscles, anthropomorphic robots, artificiallimbs, or other bionic actuators. The electrothermal composite materialand the electrothermal actuator can also be used for micro-lens focusingsystems, fluid control valves, dynamic braille, or other multifunctionactuators.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Any elements describedin accordance with any embodiments is understood that they can be usedin addition or substituted in other embodiments. Embodiments can also beused together. Variations may be made to the embodiments withoutdeparting from the spirit of the disclosure. The above-describedembodiments illustrate the scope of the disclosure but do not restrictthe scope of the disclosure.

What is claimed is:
 1. A method for making an electrothermal actuatorcomprising: providing a carbon nanotube paper, wherein the carbonnanotube paper comprises a plurality of carbon nanotubes extending alongthe same direction and joined end to end by van der Waals attractiveforce, and a density of the carbon nanotube paper is greater than orequal to 0.5 g/cm³; forming a patterned carbon nanotube paper by cuttingthe carbon nanotube paper along a cutting-line, wherein an angle betweenan extending direction of the plurality of carbon nanotubes and at leasta portion of the cutting-line is in a range from about 45 degrees toabout 90 degrees, the cutting-line is a curved line and extends along afirst direction and a second direction, the first direction isperpendicular to the second direction, a first angle between theextending direction of the plurality of carbon nanotubes and the firstdirection is about 45 degrees, and a second angle between the extendingdirection of the plurality of carbon nanotubes and the second directionis about 45 degrees; electrically connecting at least two electrodes tothe patterned carbon nanotube paper; and forming a flexible polymerlayer on the patterned carbon nanotube paper, wherein the patternedcarbon nanotube paper is at least partly embedded into the flexiblepolymer layer, a thickness ratio of the patterned carbon nanotube paperand the flexible polymer layer is in a range from about 1:7 to about1:10, and a thermal expansion coefficient of the flexible polymer layeris greater than or equal to ten times that of the patterned carbonnanotube paper.
 2. The method of claim 1, wherein the thermal expansioncoefficient of the flexible polymer layer is greater than or equal toone hundred times that of the patterned carbon nanotube paper.
 3. Themethod of claim 1, wherein a thickness of the carbon nanotube paper isin a range from about 30 micrometers to about 50 micrometers.
 4. Themethod of claim 1, wherein a thickness of the flexible polymer layer isranged from about 270 micrometers to about 450 micrometers.
 5. Themethod of claim 1, wherein the density of the carbon nanotube paper isin a range from about 0.5 g/cm³ to about 1.2 g/cm³.
 6. The method ofclaim 1, wherein a conductivity of the patterned carbon nanotube paperalong the first direction and the second direction are both in a rangefrom about 1000 S/m to about 6000 S/m.
 7. The method of claim 1, whereinthe forming the flexible polymer layer on the patterned carbon nanotubepaper comprises: putting the patterned carbon nanotube paper in a mold;injecting a flexible polymer prepolymer, which is in a viscous-liquidstate, into the mold, wherein the patterned carbon nanotube paper iscompletely immersed in the flexible polymer prepolymer; and solidifyingthe flexible polymer prepolymer to form the flexible polymer layer. 8.The method of claim 7, wherein the putting the patterned carbon nanotubepaper in the mold comprises coating a release agent on an inner surfaceof the mold.
 9. The method of claim 7, wherein the flexible polymerprepolymer is deaerated before solidifying.
 10. A method for making anelectrothermal actuator comprising: providing a carbon nanotube paper,wherein the carbon nanotube paper comprises a plurality of carbonnanotubes extending along the same direction and joined end to end byvan der Waals attractive force, and a density of the carbon nanotubepaper is greater than or equal to 0.5 g/cm³; forming a patterned carbonnanotube paper by cutting the carbon nanotube paper along acutting-line, wherein an angle between an extending direction of theplurality of carbon nanotubes and at least a portion of the cutting-lineis in a range from about 45 degrees to about 90 degrees, thecutting-line is a curved line and extends along a first direction and asecond direction, the first direction is perpendicular to the seconddirection, a first angle between the extending direction of theplurality of carbon nanotubes and the first direction is about 90degrees; and a second angle between the extending direction of theplurality of carbon nanotubes and the second direction is about 0degrees; electrically connecting at least two electrodes to thepatterned carbon nanotube paper; and forming a flexible polymer layer onthe patterned carbon nanotube paper, wherein the patterned carbonnanotube paper is at least partly embedded into the flexible polymerlayer, a thickness ratio of the patterned carbon nanotube paper and theflexible polymer layer is in a range from about 1:7 to about 1:10, and athermal expansion coefficient of the flexible polymer layer is greaterthan or equal to ten times that of the patterned carbon nanotube paper.11. The method of claim 10, wherein a first conductivity of thepatterned carbon nanotube paper along the first direction is ranged fromabout 1000 S/m to about 6000 S/m, and a second conductivity of thepatterned carbon nanotube paper along the second direction is greaterthan 6000 S/m.
 12. A method for making an electrothermal actuatorcomprising: providing a carbon nanotube paper, wherein the carbonnanotube paper comprises a plurality of carbon nanotubes extending alongthe same direction and joined end to end by van der Waals attractiveforce, and a density of the carbon nanotube paper is greater than orequal to 0.5 g/cm³; forming a patterned carbon nanotube paper by cuttingthe carbon nanotube paper along a cutting-line, wherein an angle betweenan extending direction of the plurality of carbon nanotubes and at leasta portion of the cutting-line is in a range from about 45 degrees toabout 90 degrees; electrically connecting at least two electrodes to thepatterned carbon nanotube paper; and forming a flexible polymer layer onthe patterned carbon nanotube paper, wherein the patterned carbonnanotube paper is at least partly embedded into the flexible polymerlayer, a thickness ratio of the patterned carbon nanotube paper and theflexible polymer layer is in a range from about 1:7 to about 1:10, and athermal expansion coefficient of the flexible polymer layer is greaterthan or equal to ten times that of the patterned carbon nanotube paper.